Ligand Effects of 2-(2-Pyridyl)benzazole−Pd Complexes on the X-ray Crystallographic Structures, 1H NMR Spectra, and Catalytic Activities in Mizoroki−Heck Reactions

Abstract

A series of PdCl2 complexes were synthesized using four 2-(2-pyridyl)benzazoles, namely 2-(2-pyridyl)benzimidazole (1a), 2-(2-pyridyl)benzoxazole (2a), 2-(2-pyridyl)benzothiazole (3a), and 2-(2-pyridyl)-N-methylbenzimidazole (4a). Their structures were analyzed using single X-ray crystallography, whereas the extent of the ligand dissociation were determined in solution by 1H NMR spectroscopy. Among the catalysts, 2-(2-pyridyl)benzimidazole−PdCl2 (1b) complex exhibited the highest catalytic activity toward the Mizoroki−Heck reaction: the diminished catalytic activities of 2-(2-pyridyl)benzoxazole−PdCl2 (2b) and 2-(2-pyridyl)benzothiazole−PdCl2 (3b) can be attributable to the ease of their ligand dissociation.